First, Call for a meetings. They can vary from only 1 person to thousands based on message and audience appropriate. It is up to you to maximize every minute of the time spent to have dialogue. Make sure it is a dialogue and not a monologue. It is the best way as you have the verbal and non verbal cues that enhance the communication and avoid misinterpretation.
Second, Making Conference calls. These days this is the most common as it does not require the time and expense of travel. The dialogue can take place though its dependant on voice intonation and clarity of the verbal message. They only require cost of phone call and there are many paid and free services that will facilitate use of a conference call line for many people to dial into. It’s also a common way for classes to be recorded and replayed when it’s convenient for you.